Purification of p-dioxenes by azeotropic distillation with water



United States Patent 3,399,215 PURIFICATION OF p-DIOXENES BY AZEOTROPICDISTILLATION WITH WATER Walter H. Brader, Jr., Houston, Tex., assignorto Jefferson Chemical Company, Inc., Houston, Tex., a corporation ofDelaware No Drawing. Original application Apr. 15, 1965, Ser. No.448,275. Divided and this application Nov. 13, 1967, Ser. No. 682,534

5 Claims. (Cl. 260--340.6)

ABSTRACT OF THE DISCLOSURE A crude p-dioxene is purified by diluting thecrude p-dioxene with water, distilling the mixture to obtain and collecta p-dioxene-water azeotrope, separating the azeotrope into a water phaseand a p-dioxene phase, drying the p-dioxene phase, adding a drying agentthereto and then fractionally distilling to obtain a pure p-dioxeneproduct.

Reference to other applications This application, a division ofcopending application Serial No. 448,275 filed April 15, 1965, andentitled Preparation of p-Dioxenes, is directed to the method ofpurifying p-dioxenes disclosed and claimed therein.

Description of the preferred embodiment Because of the closeness of theboiling points of the components of the reactor efiluent thepurification of the p-dioxene product is difiicult. However, I foundthat the p-dioxene can be readily purified by adding sufficient water tobring the total water content to an amount at least equivalent to thatneeded for the p-dioxene-water azeotrope. The distillation is thencarried out at atmospheric pressure and the azeotrope collected. Thedioxene phase is separated, dried. If 'a colorless product is desired asmall quantity of a hydrogenation agent such as an-alkali metalborohydride or alkali metal aluminum hydride is added and the p-dioxen'eis fractionated by distillation to give a pure, colorless product. Onlya very small amount of reducing agent, ranging from a finite amount toabout 0.5 wt. percent based on the p-dioxene present, is needed.

The dioxene phase may be dried by any known technique after separationfrom the azeotrope. For example, it may be dried by the use of molecularsieves, solid dry- .ing agents or azeotroping with benzene. The lastmethod is probably the most practical on a commercial scale.

This invention is concerned with the purification of p-dioxenes. Moreparticularly, this invention is concerned with the preparation ofp-dioxenes from diglycols by a catalytic process which involves bothdehydration and dehydrogenation.

The p-dioxenes are relatively new cyclic olefins. In United StatesPatent 3,072,623, it is disclosed that the simplest member of theseries, p-dioxene, can be polymerized to yield a polymer having amelting point in excess of 250 C. and a partial water solubility.

Heretofore, p-dioxene has been prepared by the reaction of an aliphaticGrignard reagent with 2,3-dichlorodioxane as shown by the followingequation:

RMgCl RC1 MgClg C1 0 0 While this reaction is satisfactory for preparingsmall quantities of p-dioxene, it is not suitable for use in acommercial operation.

In United States Patent 2,807,629, the dehydrogenation of diethyleneglycol is shown to yield p-dioxanone.

3,399,215 Patented Aug. 27, 1968 ICE A similar treatment of higheraliphatic diglycols results in a formation of some substitutedp-dioxene.

The dehydrogenation of diethylene glycol to p-dioxanone is believed toinvolve an intermediate hemiacetal as shown below:

It is known that secondary alcohols dehydrogenate faster than primaryalcohols; thus, one skilled in the art would expect the intermediatep-dioxanol to dehydrogenate more rapidly than would the primary hydroxylgroup of diethylene glycol and, thus, p-dioxanone is the expectedproduct.

A method for the preparation of p-dioxenes from diglycols containingprimary and/ or secondary hydroxyl groups is disclosed by Summerbell etal. in an article entitled, Copper Chromite-Catalyzed Conversion of SomeGlycols to Dioxenes (Journal of Organic Chemistry, 1962, vol. 27, pages4433-4436). In accordance with this process, the diglycol is reacted inthe vapor phase at a temperature within the range of about 250 to about350 C. over a catalyst which is a combination of a metallicdehydrogenation catalyst with a dehydration catalyst. It is believed tobe this dual dehydrogenation-dehydration character of the catalyst thatleads to the unexpected results described herein.

Metallic dehydrogenation catalysts are well known to those skilled inthe art. Generally, such catalysts include, but are not limited to, themetals or oxides of the metals of Groups I-b and VIII. Examples of suchdehydrogenation catalysts include copper, silver, gold, nickel, zinc,platinum, palladium, cobalt, and the oxides thereof. The oxides ofcopper are preferred, particularly cupric oxide.

It is to be understood that when a metallic oxide is used, somereduction occurs under the conditions of the reaction. Thus, when it issaid that cupric oxide is the preferred catalyst, it is to be understoodthat the catalyst will be a mixture of metallic copper, cuprous oxideand cupric oxide after the reaction has proceeded for a short time.

Dehydration catalysts are also well known to those skilled in the art.Examples of dehydration catalysts include alumina, silica,silica-alumina, magnesia, activated clays, aluminum phosphate, ironphosphate, etc.

The relative amount of each type catalyst to be used will depend uponthe particular catalyst pair employed. For a given catalyst pair, theproper amount of each to be used can be readily determined by runningtwo or three brief experiments such as are described in the examples. Ingeneral, it may be said that the catalyst will comprise from about toabout 1 wt. percent dehydrogenation catalyst and, correspondingly, fromabout 25 to about 99 Wt. percent dehydration catalyst.

The reaction should be conducted in the vapor phase at a temperaturewithin the range of about 250 to about 350 C. The liquid diglycol is fedto the reactor at a space velocity of from about 0.5 to about 3.0 cc. ofdiglycol per hour per cc. of catalyst. A carrier gas is preferablyemployed at a space velocity of 100 to 500 cc. per hour per cc. ofcatalyst. The preferred carrier gases are air, oxygen, or mixtures ofnitrogen and oxygen; however, other gaseous materials such as hydrogenor nitrogen may also be used.

The invention will be further illustrated by the following examples. Theexamples were conducted in a cylindrical stainless steel reactor withdimensions of 1 X 30 inches. The reactor tube was surrounded by a 4-inchjacket, to which jacket was attached a condenser and liquid returnsystem. The jacket was filled with a heat transfer liquid and thereactor temperature was controlled by adjusting the pressure above therefluxing liquid. The reactor was packed so that from 100-200 cc. ofcatalyst were held in the center of the reaction tube and the area abovethe catalyst was filled with inert material to act as a preheater. Thediglycol and carrier gas were introduced at the top of the reactor. Thereactants were allowed to flow through the reactor and were collected ina flask to which was attached a Dry Ice-acetone condenser The collectedproduct was transferred to a column and fractionated.

In a typical experiment diethylene glycol was pumped at a space velocityof one cc./cc. catalyst/hour and air metered at 120 cc. gas/cc.catalyst/hour into the top of the reactor. The reactants flowed downwardthrough the reactor and collected in a round-bottom flask which wasimmersed in a Dry Ice-acetone bath and to which was attached a DryIce-acetone condenser. Reactions were usually carried out for a periodof 4-6 hours.

To the product so obtained was added suflicient water to azeotrope allof the p-dioxene, and the product was distilled at atmospheric pressure.The water-p-dioxene azeotrope was collected (B.P. 79 C.), the phaseswere separated and the organic phase was dried. In order to dischargethe yellow color of the dry p-dioxene a few grams of sodium borohydridemay be added and the mixture distilled to give pure, colorlessp-dioxene.

For pure p-dioxene, the boiling point was 93 C., the refractive indexwas 1.4320 at 30 C. and the specific gravity was 1.084 at 20 C.; thewater azeotrope boiled at 79 C. The S-methyl-p-dioxene azeotrope boiledat 86 C. and the Z-methyl-p-dioxene azeotrope boiled at 99 C.

EXAMPLE I Diethylene glycol (1,775 grams) was pumped at a space velocityof 1 into the reactor filled with 110 cc. of copper oxide on an activealumina support and held at 290 C. Concurrent with the feed, air waspassed at a vapor space velocity of 150-300 cc. per hour per cc. ofcatalyst. Under these conditions a diethylene glycol conversion of 82%was obtained with a p-dioxene yield of 40 mol percent and a p-dioxeneyield of 47 mol percent.

EXAMPLE II In this example, a dehydrogenation catalyst was used withouta dehydration carrier. In essentially the same manner as in Example I,except that no carrier 'gas was used, 527 grams of diethylene glycol wasconverted over 100 cc. of copper chromite catalyst (80% copper oxide,17% chromia) in a reactor held at 295 C. The conversion of diethyleneglycol was 83% and a yield of pdioxanone of 81 mol percent was obtained.No p-dioxene or p-dioxane was observed.

EXAMPLE III Example I was repeated except that hydrogen was used toreplace the air as a carrier gas. The diethylene glycol conversion was88%, the p-dioxene yield was 31 mol percent, the p-dioxane yield was 35mol percent and the p-dioxanone yield was 28 mol percent.

EXAMPLE IV In essentially the same manner as in Example I, diethyleneglycol was converted over a copper oxide on activated clay catalyst.Conversion of diethylene glycol was 31% with a p-dioXene yield of 45 molpercent, a p-dioxane yield of 10 mol percent and a p-dioxanone yield of6 mol percent.

EXAMPLE V In essentially the same manner as in Example I,3-oxahexane-1,5-diol was converted over a 10% copper oxide on activealumina catalyst. The conversion was 87% and the yield ofZ-methyldioxene was 52 mol percent, the yield of S-methyldioxene was 22mol percent and the yield of 2-rnethyldioxane was 5 mol percent.

Because of the closeness of the boiling points of the components of thereactor effluent the purification of the p-dioxene product is difficult.However, I found that the p-dioxene can be readily purified by addingsufiicient water to bring the total water content to an amount at leastequivalent to that needed for the p-dioxene-water azeotrope. Thedistillation is then carried out at atmospheric pressure and theazeotrope collected. The dioxene phase is separated, dried. If acolorless product is desired, a small quantity of a hydrogenation agentsuch as an alkali metal borohydride or alkali metal aluminum hydride isadded and the p-dioxene is fractionated by distillation to give a pure,colorless product. Only a very small amount of reducing agent, rangingfrom a finite amount to about 0.5 wt. percent on the p-dioxene present,is needed.

The dioxene phase may be dried by any known technique after separationfrom the azeotrope. For example, it may be dried by the use of molecularsieves, solid drying agents or azeotroping with benzene. The last methodis probably the most practical on a commercial scale.

In accordance with my process, diglycols having the formula:

0 oR oHR CHR CHR OH OH may be selectively converted to the correspondingp-dioxene regardless of whether the hydroxyl groups involved are primaryor secondary hydroxyl groups. The p-dioxcues that can be obtained willthus be those having the formula:

the formula:

0 R- R Bi IR 0 wherein each R is selected from the group consisting ofhydrogen and C -C alkyl groups which comprises adding to the crudep-dioxene an amount of water suffi'cient to form an azeotrope with saidpdioxene, distilling said mixture and collecting said azeotrope andseparating the p-dioxene phase from the aqueous phase of said azeotrope,and fractionally distilling said p-dioxene phase to give a pure product.

2. In a method for the preparation of a p-dioxene having the formula:

0 R1 TR R R 0 each R being selected from the group consisting ofhydrogen and C -C alkyl groups, wherein the corresponding diglycol iscontacted in the vapor phase at a temperature within the range of about250 to about 350 C., at a space velocity of from about 0.5 to about 3.0cc. of liquid feed per hour per cc. of catalyst with a catalyst whichcomprises from about 1 to about 75 wt. percent of a metallicdehydrogenation catalyst and, correspondingly, from about 99 to about 25wt. percent of a dehydration catalyst, the improvement which comprisescollecting the effluent from the reaction, adding an amount of watersufficient to form an azeotrope with said p-dioxene, distilling saidmixture, collecting said azeotrope, separating the p-dioxene phase ofsaid azeotrope from the aqueous phase thereof, drying said p-dioxenephase, adding a hydrogenating agent and fractionally distilling saidp-dioxene phase to obtain a pure p-dioxene product.

References Cited UNITED STATES PATENTS 9/1964 Guest 260340.6

OTHER REFERENCES Summerbell et al.: Journal of Organic Chemistry, vol.27 (1962), pp. 4433-4436.

3. A method as in claim 2 wherein the dehydrogena- 15 WILBUR BASCOMB JR"Primary Exammen tion catalyst is cupric oxide.

